The present invention relates to an improved cyanide-free copper electrolyte and process, and more particularly to an improved electrolyte and process for electrodepositing copper in the form of an adherent, ductile, fine-grained copper plate on a variety of conductive substrates.
A variety of cyanide-free copper electrolytes have heretofore been used or proposed for use as replacements for the well-known and conventional commercially employed cyanide-containing counterparts. Typical of such processes are those described in U.S. Pat. Nos. 3,475,293; 3,706,634; 3,706,635; 3,833,486 and 3,928,147. A particularly satisfactory electrolyte composition and process for electrodepositing copper is described in U.S. patent application Ser. No. 551,135, filed Nov. 16, 1983 for "Cyanide-Free Copper Plating Process and Alloy Anode" (now U.S. Pat. No. 4,462,874), which is assigned to the same assignee as the present invention.
While the electrolytes and processes as described in the aforementioned United States patents have provided satisfactory copper electrodeposits under carefully controlled operating conditions, such electrolytes and processes have been found deficient from a commercial standpoint due to the wide disparity between the anode efficiency and cathode efficiency during electrodeposition. The foregoing problem is aggravated when high anode current densities are employed causing the anodes to become polarized. Under such conditions, a rapid depletion of the copper ion concentration in the electrolyte occurs accompanied by the formation of deleterious breakdown products in the electrolyte which detracts from optimum performance. A further problem encountered in connection with such prior art electrolytes is the coarse grain structure obtained under certain electroplating conditions particularly when heavy copper deposits are applied detracting from the application of a subsequent decorative copper or nickel overplate to provide a final article of the desired appearance.
The present invention overcomes the foregoing problems and disadvantages by providing an improved cyanide-free electrolyte in which the anode efficiency is substantially increased enabling electrodeposition at relatively higher average cathode current densities without encountering any tendency of the anodes to polarize while simultaneously enhancing the brightness of the copper electrodeposit and an improvement in grain refinement and uniformity of the copper deposit.